The present invention relates to a method of making through-passages in sheet metal parts.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
European patent document EP 2 000 335 A2 describes a method of making an axle component which is composed from a longitudinal profile of sheet metal and is formed on both ends with a bearing receptacle, respectively. The longitudinal profile is a single-piece U-shaped press shell with a first wall side which is traversed by the bearing receptacles and in opposition to the first wall side a second wall side which is traversed by bearing receptacles. The axle components is made by first cutting the metal sheet to size and then angling the metal sheet by 90° in relation to the edge support that has been shaped beforehand to form a first wall side. The first wall side is holed in the area of the later bearing receptacle. Through-passages are then formed at the holes. Thereafter, the second wall side is angled by 90° in relation to the edge support so that the wall sides are positioned in direct opposition. The second wall side is then holed in the area of the later bearing receptacles and provided with a through-passage. A rubber-metal bearing is later placed in these holes. In this manufacturing sequence, the first through-passage is made before the second wall side is angled by 90° and disposed in opposition to the first wall side. As a consequence of the manufacturing process, the through-passage and thus the collars point outwards, i.e. away from one another.
Sheet metal parts involved here are often used as links of multilink suspensions for motor vehicles and considered articles of mass production. Thus, when production of a certain minimum number is involved, the manufacturing process should be cost-efficient and quick in order to be economically viable. Transfer tools or follow-on composite tools are typically used for this purpose. In a follow-on composite tool, a sheet metal blank is advanced incrementally until a series of successive tool stations has been passed. This is normally implemented in a single forming press with sufficiently large tool table. At the end of the forming process, the workpiece is separated from the so-called carrier strip and cut in pieces. In a transfer tool, single sheet metal blanks are cut in a cutting station and then transported by suitable grippers or by a transfer device which is coupled with the press step by step or from tool set to tool set. Also used are hand insertion sets in which the workpiece is moved by hand from tool set to tool set.
Regardless whether transfer tools or follow-on composite tools are used, the realization in U-shaped metal sheets of inner through-passages, i.e. holes which are formed with a circumferential collar, with the collar in one leg pointing towards the collar in the opposite leg, i.e. collars that project inwardly, is difficult and requires a separate manufacturing step carried out by a special machine tool. As a result, production costs are increased.
It would therefore be desirable and advantageous to provide an improved method of making inner through-passages in U-shaped sheet metal parts to obviate prior art shortcomings in a cost-efficient and reliable manner.